Answer:
Option D.

Step-by-step explanation:
The area of the circular bases is:

Where
is the radius of the circle
Then


The area of the rectangle is:

Where

b is the width of the rectangle and
is the length
Then the area of the rectangle is:


Finally the total area is:


The surfaces are the faces of the prism. The vertices are the points of the prism, where three sides intersect. You can also call them corners. To find the volume, you multiply length and width and height.
For the largest area, half the fence is used parallel to the river, and the other half is used for the two ends of the rectangular space.
The dimensions are 475 m by 237.5 m.
_____
Let x represent the length along the river. Then the area (A) is found as
.. A = x*(950 -x)/2
This equation describes a parabola with its vertex (maximum) halfway between the zeros of x=0 and x=950. That is, the maximum area is achieved when half the fence is used parallel to the river.